1. Field of the Invention
The present invention relates to a lens barrel for use in an image pickup apparatus, such as a digital camera, and more particularly to a collapsible zoom lens barrel configured to perform photographic lens extension and retraction in a so-called digital camera and the construction of an image pickup apparatus including the zoom lens barrel.
2. Description of the Related Art
As a collapsible zoom lens mechanism for extending and retracting a lens barrel, which is used in a digital camera or the like, there has been known a method using cams. This method uses a lens barrel held in a manner movable along an optical axis with its rotation restricted, and a rotary barrel formed with a cam groove. More specifically, a follower pin provided in the lens barrel is slidably fitted in the cam groove formed in the rotary barrel, whereby the lens barrel can be moved in the optical axis direction, following the profile line (path) of the cam groove in accordance with rotation of the rotary barrel. Thus, at the time of shooting, a photographic lens is extended to a predetermined position, whereas at the time of non-shooting, the lens barrel is retracted into a body of the digital camera.
In recent years, it has been strongly demanded to achieve a higher optical zoom magnification and reduction of thickness of a zoom lens barrel in a digital camera. For this reason, in a case where a digital camera is configured such that its lens barrel is housed in the body of the digital camera at the time of non-shooting, it is becoming difficult to extend its photographic lens over a sufficient distance at the time of shooting only by the above-mentioned method using a cam.
To solve this problem, there have been proposed a first mechanism and a second mechanism mentioned below as examples of a mechanism for extending and retracting a lens barrel. The first mechanism is configured such that an optical element-holding member and an optical element-driving member are urged in a predetermined direction by a spring member, and when a lens barrel is to be retracted, the optical element-holding member and the optical element-driving member are caused to perform pivotal motion relative to each other in a direction against the urging force of the spring member (see Japanese Patent Laid-Open Publication No. 2008-26716). On the other hand, the second mechanism is configured such that a barrier opening and closing device is provided with a cam projection, and the barrier opening and closing device is rotated when barrier blades are open, whereby the cam projection causes a lens holding frame, via a slide pin of the same, to project from a shooting opening (see Japanese Patent Laid-Open Publication No. 2007-248608).
However, in the technique described in Japanese Patent Laid-Open Publication No. 2008-26716, there is a fear that when an external force acts, the optical element-holding member can fall out from the lens barrel.
In the technique described in Japanese Patent Laid-Open Publication No. 2007-248608, since the barrier opening and closing device is interposed between a movable barrel and the lens holding frame, there is a fear that dimensional error is increased or lens positioning accuracy is degraded.